Research ArticleA Compact CPW-Fed Low-Profile Wideband Circularly PolarizedSlot Antenna with a Planar Ring Reflector for GNSS Applications

Jiade Yuan , Yujie Li , Zhimeng Xu, and Jiamin Zheng

College of Physics and Information Engineering, Fuzhou University, Fuzhou 350116, China

Correspondence should be addressed to Jiade Yuan; yuanjiade@fzu.edu.cn

Received 19 July 2019; Revised 23 September 2019; Accepted 30 September 2019; Published 31 October 2019

Academic Editor: Giorgio Montisci

Copyright © 2019 Jiade Yuan et al. *is is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A compact low-profile wideband circularly polarized slot antenna for global navigation satellite system (GNSS) is presented. *eantenna comprises a planar slot radiator with a coplanar waveguide (CPW) feed and a modified ring-shaped reflector to achieveunidirectional radiation. *e modified reflector is an inner square patch with four slantly cut corners, a center ring, and an outerring with a notch; they significantly reduce the separation between the antenna radiator and reflector and therefore the overallantenna height. *e overall dimensions are λ0/3× λ0/3× λ0/30 (λ0 denotes the free space wavelength at lower frequency). *emeasured − 10 dB bandwidth of |S11|, 3-dB axial ratio (AR) bandwidth, and maximum gain are of 1.53–2.28GHz, 1.558–1.672GHz, and 5.87 dBi, respectively. *e proposed antenna is simple without any additional feeding networks orshorting probes.

1. Introduction

Handheld terminals of global navigation satellite system(GNSS) have been popular in emergency communication,such as inshore fishery, emergency rescue, and forest fireprevention. As a key component, the antennas of the ter-minals not only have to be of small size, low profile, andunidirectional radiation but also must have a wide bandwidthto cover the multiple frequency bands of GNSS, such as GPSL1 (1575.42± 1.023MHz), BDS B1 (1561.098± 5MHz), andGLONASS L1 (1602.5± 4MHz) [1, 2].

Various techniques to broaden antenna bandwidth ofunidirectional radiation antenna have been reported. In[3–6], parasitic patches or coupling feed structure is appliedto increase bandwidth. *e antenna bandwidth is increasedusing four parasitic strips and a capacitive-coupled feed in[3], using a Γ-shaped coupling feed structure in [4], using atapped coupling line in [5], and using four feed stripscoupling with the slot cavity in [6]. In [7], the broadband of acircularly polarized directional antenna is achieved with acircular radiating patch, a ground plane, and a novel cou-pling feeding network. *e slot antenna’s ARBW and IBWcover the frequency band of 75.8% (1.13–2.51GHz). In [8], a

circular polarized antenna with an IBW of 0.900–2.95GHzand ARBW of 1.0–2.87GHz is developed. *e antenna iscomposed of two orthogonally placed elliptical dipolesprinted on both sides of a substrate. In [9], a novel widebandtechnique is presented based on the mode analysis and thebandwidth is expanded by loading a folded shorting pin.*eoperating frequency covers the band of 1.1–1.6GHz. *eantenna has an overall size of only 0.4 λ0 × 0.4 λ0 × 0.05 λ0when the relative permittivity of the substrate is 6. In [10],the antenna is proposed and has the IBW of 1.02 to 2.18GHzand ARBWof 1.15 to 2GHz using four claw-shaped parasiticbranches. Although the abovementioned antennas havewide bandwidths and good directional radiation pattern,they have relatively larger size or complicated feedingnetwork. As a result, they are not suitable for uses inhandheld devices and for mass production.

In recent years, new antennas of simpler structures thathave excellent IBW and ARBW have been reported [11–16].In [11], a coplanar waveguide- (CPW-) fed square slotantenna is presented where an L-shaped feedline and arectangle-shaped parasitic element is used to obtain the IBWof 63.97% and ARBW of 48.28%. In [12], by embedding apair of inverted L-shaped strips and loading two spiral slots

HindawiInternational Journal of Antennas and PropagationVolume 2019, Article ID 6463101, 12 pageshttps://doi.org/10.1155/2019/6463101

in the ground plane, the high IBW and ARBW of 111% and56% are achieved, respectively. In [13], instead of using theCPW feed, the microstrip line feed is employed in the slotantenna and a transverse strip is used in the ground plane;they lead to the IBW and ARBW of 90.2% and 40%, re-spectively. In [14], a horseshoe-shaped slot and twoL-shaped radiators are introduced, and the IBW and ARBWare of 113% (0.7–2.52GHz) and 60.2% (3.47–6.46GHz),respectively. Although presenting distinct advantages inIBW and ARBW, these antennas have undesirable bi-directional radiation patterns. To obtain a unidirectionalradiation pattern, a simple conducting plane is placed un-derneath the CPW-fed slot antenna without changing itsoriginal structural dimensions [16–19]. However, they allneed a relatively large distance between the radiators and theconducting planes and fail to meet the requirements of lowprofile.

In this paper, to overcome the shortcomings of theexisting antennas for GNSS systems, we propose the in-tegration of a broadband slot antenna with a modified re-flector to form a new compact low-profile antenna that has awide bandwidth and unidirectional radiation pattern. It hasthe smallest volume size among the antennas reported so farwith an easy and simple coplanar waveguide (CPW) feed. Anevolutional approach is presented to show the step-by-stepdevelopment of the proposed antenna and its operationalprinciples; the approach may also be used for any futuredevelopments of new antennas.

2. Configuration and Design of theProposed Antenna

*e cross-sectional view of the proposed slot antenna isshown in Figure 1(a): there are two layers of FR4 substrateseparated by air; the radiator and reflector are printed on theupper and lower FR4 substrate layers, respectively.

*e top view of the radiator on the upper layer is shownin Figure 1(b). *e antenna is fed by a 50 ohm coplanarwaveguide (CPW) of a strip width of Ws and the gaps of gs

with the ground. *e strip becomes wider as it extendsfurther into the center of the patch with a wider width ofW1. Four grounded rectangular patches with differentwidths of A1,W3, L2, and A3 are etched on the top and rightsides, respectively. A grounded T-shaped strip with thedimension of L5, W5, and W6 is made on the left side. *egeometry of the radiator (Figure 1(b) is evolved from asimple monopole antenna with a grounded loop, asexplained in Section 2.1 later. *e bottom view of thereflector is shown in Figure 1(c); the reflector comprises ofan outer ring, a center ring, and an inner square patch withits four symmetrical corners cut slantly. A notch is etchedin the outer ring.

*e combination of the radiator placed on the upperlayer and the reflector placed on the lower layer forms theproposed low-profile antenna with wide IBW and ARBW.*e radiator and reflector should be considered anddesigned simultaneously because there is strong mutualcoupling between them due to a small height h of about λo/30 (Figure 1(a)). In other words, the performance of the

radiator is jointly affected by the radiator and the reflector.*is is different from the conventional antenna presented in[16–19] where the reflector and the radiator could bedesigned relatively independently. In addition, through itsembedded structures, such as the grounded rectangularpatches and the T-shaped strip, the radiator generates or-thogonal electric fields, which then lead to the circularpolarization with the unidirectional radiation (achieved withthe reflector).

*e optimized dimensions of the proposed antenna areobtained through simulation using the ANSYS HFSS 18, andthe results are listed in Table 1.

2.1. Evolution and the Design Steps of the Proposed Antenna.Six steps (Antennas I–VI) are shown in Figure 2 to explainthe evolution and design process of the proposed antenna.*e overall size of all the antennas is kept unchanged. *esimulated results of |S11|, AR at the boresight, and radiationpattern at f� 1.575GHz of Antennas I–VI are presented inFigures 3(a)–3(c), respectively.

Antenna I is a conventional coplanar slot antenna, andthe reflector is a square-shaped conducting plane. It has poorperformances in |S11|, AR, and unidirectional radiationbecause of the strong influence from the reflector on theradiator. Antenna II is Antenna I with the addition of a ringslot being etched in the reflector; |S11| and the directivity ofthe radiation pattern become better. *e reasons are that theetched slots reduce electromagnetic coupling between theradiator and the reflector and the resulting current distri-butions improve the impedance matching and unidirec-tional radiation. Antenna III is Antenna II with an outer ringslot and a notch being etched in the reflector that forms theinner patch, center ring, and outer ring. *e notch in thereflector reduces the Q factor due to the close distancebetween the reflector and the SMA connector on radiator.Antenna III has better directivity than Antenna II because ofthe introduction of the outer slot that further optimizes thecurrent distribution. From Antenna I to Antenna III, onlythe reflector is changed and the radiator is symmetric aboutthe central strip of the CPW feed; hence, they lead to linearpolarization and high AR values as shown in Figure 3(b).

To achieve the circular polarization and further improvethe antenna performance, from Antenna IV to Antenna VI,the radiator is evolved, while the reflector is kept the same.Antenna IV is formed from Antenna III by embedding aT-shaped grounded strip on the left side and a rectangulargrounded patch on the top left corner. As a result, the ARperformance is improved significantly. *e reason is that thetransverse electric fields between the inverted Tstrip and thecenter strip are excited and its magnitude and phase of theelectric field can generate circularly polarized radiation.Antenna V is evolved from Antenna IV by adding a rect-angular patch and a stairstep-shaped grounding patches inthe right side and lower right corner of the Antenna IVradiator, respectively. As shown in Figures 3(a) and 3(c), |S11| and directivity improve. At last, two rectangulargrounding patches are added to the lower left corner and thetop of the radiator of Antenna V, respectively; they fine tune

2 International Journal of Antennas and Propagation

the antenna performance, and the final design of the antennaVI is formed.

2.2. Generation of Circular Polarization. *e current dis-tributions on the radiator at different time instants aresimulated and studied as time t increases from t � 0 tot � 270°/ω � 3T/4; they are shown in Figure 4 atf� 1.575GHz as a test point.

As seen from Figure 4(a), at t� 0, the predominantcurrents are J0 on the left and right sides, and they flow in thesame +y direction. As seen from Figure 4(b), at the instant oft � 90°/ω � T/4, there are four strong currents: current J0 onthe top and bottom sides that flow in the − x direction,current J1 on the T-shaped strip that flows in the − x di-rection, current J2 on the feed patch that flows in the +ydirection, and current J3 on the rectangular patch adjacent toJ2 that flows in the -y direction. J2 and J3 flow in the oppositedirections (i.e., +y and –y directions), cancelling the far fieldsgenerated by each other; J0 and J1 flow in the same direction(i.e., the − x direction), reinforcing the far fields generated byeach other. *erefore, at t � 90°/ω � T/4, the predominantcurrents are in the − x direction.

As further seen from Figures 4(c) and 4(d), the pre-dominant currents at t � 180°/ω � T/2 andt � 270°/ω � 3T/4 are equal in magnitude and opposite inphase to the currents at t � 0° /ω � T/4 and t � 90°/ω � T/2,respectively.

Table 1: Optimized geometric parameters (unit: mm).

Parm ValueG1 65.5G2 16G3 19G4 25.5G5 53G6 38d1 4.5WS 3LS 21.1gs 0.6dcut 2.2W1 6.4W2 9W3 12W4 10W5 2W6 13h 5L2 14L3 7L4 4.4L5 19L6 13.9L7 20A1 10.4A2 11A3 10

x

z

y

Air layer

Reflector

h

Plastic screw

(a)

G5

W2A1

W5

W1

W3

L3

Ws

W4

L4

W6 Ls

gs L6

L2

L5

A2

A3

G6

y

xz

CPW port(b)

G3

G2

dcut

G1

L7

yx z

d1

G4

(c)

Figure 1: *e proposed antenna. (a)*e cross-sectional view of the antenna, (b) the (top) view of the radiator, and (c) the (bottom) view ofthe reflector.

International Journal of Antennas and Propagation 3

Antenna I Antenna III Antenna VI Antenna IV Antenna V Antenna II

Radiator I Radiator II Radiator III Radiator IV Radiator V Radiator VI

(a)

Antenna I Antenna III Antenna VI Antenna IV Antenna V Antenna II

Reflector VIReflector I Reflector VReflector IVReflector IIIReflector II

(b)

Figure 2: Evolution and the design steps of the proposed antenna, from Antennas I to VI. (a) *e radiator on the upper layer and (b) thereflector on the lower layer.

|S11

| (dB

)

–20

–10

0

1.4 1.6 1.8 2.0 2.2 2.41.2Frequency (GHz)

Antenna IAntenna IIAntenna III

Antenna IVAntenna VAntenna VI

(a)

1.55 1.60 1.65 1.70 1.751.50Frequency (GHz)

06

121824303642485460

AR

(dB)

Antenna IAntenna IIAntenna III

Antenna IVAntenna VAntenna VI

(b)

Antenna IAntenna IIAntenna III

Antenna IVAntenna VAntenna VI

–9

–6

–3

0

3

60

30

60

90

120

150180

210

240

270

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330

–6

–3

0

3

6

(c)

Figure 3: Simulated reflection coefficient |S11| and axial ratio of Antennas I–VI. (a) |S11|, (b) axial ration, and (c) radiation pattern.

4 International Journal of Antennas and Propagation

Consequently, the vector sum of the predominantcurrents flows in the anticlockwise direction with time asshown in Figure 4. Such current variations with time resultin predominantly a right-hand circular polarization (RHCP)wave radiations in the z> 0 half spaces.

3. Parametric Studies

Parametric studies are performed by simulation of the an-tenna parameters of |S11| and AR; the results allow opti-mization and final design of the proposed antenna. Unlessindicated otherwise, only one geometrical parameter isvaried each time, and the rest of the parameters are keptunchanged in the following investigations.

3.1. Dimensions of the Center Strip (or Feedline) (Ls and W1).|S11| and AR at the boresight of the proposed antenna areaffected by the dimensions of the central strip of the CPWfeed. Its length and width are denoted as Ls and W1, re-spectively. Simulation results are shown in Figures 5(a) and5(b). When W1 � 6.4mm and Ls varies from 19.1mm to23.1mm, both |S11| and AR first become better and thenworse. When W1 increases from 4.4mm to 8.4mm with

fixed Ls � 21.1mm, |S11| has slight variations while AR variessignificantly and the frequency of the lowest AR value (indB) increases. *e reason is that W1 impacts directly thedistribution of transverse electric fields in the slots of theradiator and therefore affects the AR. *e optimal value isLs � 21.1mm andW1 � 6.4mmwith the lowest AR of 1.45 dBat the frequency of 1.575GHz.

3.2. Dimensions of the T-Shaped Strip (W6 and L5). |S11| andAR at the boresight of the proposed antenna are affected bythe lengths of the ground T-shaped strip, W6 and L5.Simulation results are shown in Figures 6(a) and 6(b).When L5 �19mm andW6 increases from 12mm to 14mm,|S11| has slight variation while AR shows visible changes.*is indicates that AR is more sensitive toW6; the reason isthat the transverse electric field between the T-shaped stripand the center feed strip is sensitive to the gap width(determined by W6) as it forms the one of the axial po-larizations for the circular polarization. For the similarreason, when L5 increases from 16mm to 22mm with thefixedW6 �13mm, |S11| varies slightly and AR shows visiblevariations.

J0J0

Jsurf (A/m)1. 5000E + 011. 4005E + 011. 3011E + 011. 2016E + 011. 1021E + 011. 0026E + 019. 0316E + 008. 0369E + 007. 0421E + 006. 0474E + 005. 0526E + 004. 0579E + 003. 0632E + 002. 0684E + 001. 0737E + 000. 8970E – 02

y

xz

(a)

J0

J2

Jsurf (A/m)1. 5000E + 011. 4005E + 011. 3011E + 011. 2016E + 011. 1021E + 011. 0026E + 019. 0316E + 008. 0369E + 007. 0421E + 006. 0474E + 005. 0526E + 004. 0579E + 003. 0632E + 002. 0684E + 001. 0737E + 000. 8970E – 02

J1

J0

J3

y

xz

(b)

J0 J0

Jsurf (A/m)1. 5000E + 011. 4005E + 011. 3011E + 011. 2016E + 011. 1021E + 011. 0026E + 019. 0316E + 008. 0369E + 007. 0421E + 006. 0474E + 005. 0526E + 004. 0579E + 003. 0632E + 002. 0684E + 001. 0737E + 000. 8970E – 02

y

xz

(c)

J0

J1

J0

J2

J3

Jsurf (A/m)1. 5000E + 011. 4005E + 011. 3011E + 011. 2016E + 011. 1021E + 011. 0026E + 019. 0316E + 008. 0369E + 007. 0421E + 006. 0474E + 005. 0526E + 004. 0579E + 003. 0632E + 002. 0684E + 001. 0737E + 000. 8970E – 02

y

xz

(d)

Figure 4: Simulated electric current distribution at 1.575GHz. (a) t� 0, (b) t�T/4, (c) t�T/2, and (d) t� 3T/4. T is the period of thesinusoidal fields with angular frequency ω.

International Journal of Antennas and Propagation 5

3.3. Dimension of the Inner Square Patches of the Reflector(G2). Figures 7(a) and 7(b) show the simulation results of |S11| and AR and realized gain of RHCP with the variation ofG2, respectively. It can be observed from Figure 7(a) that theresonant frequency is shifted to the lower value with theincreasing of G2 from 15mm to 17mm. *e reason can beexplained that the equivalent capacitor between the radiatorand reflector is increased because the increasing of G2 meansthe decreasing of the width of the inner slot of the reflector.Meanwhile, the AR changes to better then worse (see ARcurves in Figure 7(b)). *e realized gains of RHCP also vary

with the increasing of G2 and appear lower values whenG2 �17mm, as shown the realized gain curves in Figure 7(b).*e main reason is due to the poor AR performance whenG2 �17mm.

3.4. Dimensions of the Center Ring of the Reflector (G3 and d1).G3 and d1 (shown in Figure 1(b)) represent the relativeposition and width of the center ring in the reflector, re-spectively. Figures 8(a) and 8(b) show |S11|and AR in theoperating frequency rang with different G3 and d1. It can be

|S11

| (dB

)

–40

–30

–20

–10

0

1.4 1.6 1.8 2.0 2.2 2.41.2Frequency (GHz)

LS = 19.1mm, W1 = 6.4mmLS = 21.1mm, W1 = 6.4mmLS = 23.1mm, W1 = 6.4mmLS = 21.1mm, W1 = 4.4mmLS = 21.1mm, W1 = 8.4mm

(a)

0

3

6

9

12

15

18

21

AR

(dB)

1.55 1.60 1.65 1.70 1.751.50Frequency (GHz)

LS = 19.1mm, W1 = 6.4mmLS = 21.1mm, W1 = 6.4mmLS = 23.1mm, W1 = 6.4mmLS = 21.1mm, W1 = 4.4mmLS = 21.1mm, W1 = 8.4mm

(b)

Figure 5: Variations of (a) |S11| and (b) AR with different dimensions of center strip, Ls and W1.

|S11

| (dB

)

1.4 1.6 1.8 2.0 2.2 2.41.2Frequency (GHz)

W6 = 12mm, L5 = 19mmW6 = 13mm, L5 = 19mmW6 = 14mm, L5 = 19mmW6 = 13mm, L5 = 16mmW6 = 13mm, L5 = 22mm

–40

–30

–20

–10

0

(a)

0

3

6

9

12

15

AR

(dB)

1.55 1.60 1.65 1.70 1.751.50Frequency (GHz)

W6 = 12mm, L5 = 19mmW6 = 13mm, L5 = 19mmW6 = 14mm, L5 = 19mmW6 = 13mm, L5 = 16mmW6 = 13mm, L5 = 22mm

(b)

Figure 6: Variations of (a) |S11| and (b) AR with different dimensions of the T-shaped strip, W6 and L5.

6 International Journal of Antennas and Propagation

observed that |S11| has slight variations while AR has visiblechanges with the increase of G3 from 18mm to 20mm andthe increase of d1 from 3.5mm to 5.5mm.*is indicates thatAR is more sensitive to the variation of the relative positionand width of the center ring.

3.5. Dimensions of the Outer Ring of the Reflector (G1 and G4).|S11| and AR at the boresight of the proposed antenna withvarying lengths of the outer ring of the reflector, G1 and G4,are computed, and the results are shown in Figures 9(a) and9(b). When G1 increases from 60.5 to 70.5mm and G4 in-creases from 24.5mm to 26.5mm, |S11| has slight variations

while AR shows visible variations. *e optimal values forsmall AR and antenna size are G1 � 65.5mm andG4 � 25.5mm.

Based on the above studies, the final geometrical pa-rameters of the proposed antenna are listed in Table 1.

4. Experimental Results and Discussion

Based on the optimized parameters listed in Table 1, aprototype of the proposed antenna is fabricated, as shown inFigures 10(a)–10(c) for top, bottom, and side views, re-spectively, where the two layers are separated and supportedwith four plastic posts.

|S11

| (dB

)

–40

–30

–20

–10

0

1.4 1.6 1.8 2.0 2.2 2.41.2Frequency (GHz)

G2 = 15mmG2 = 16mmG2 = 17mm

(a)

0

3

6

9

12

15

AR

(dB)

1.55 1.60 1.65 1.70 1.751.50Frequency (GHz)

–8

–4

0

4

8

Real

ized

gai

n (d

Bi)

G2 = 15mmG2 = 16mmG2 = 17mm

(b)

Figure 7: Variations of (a) |S11| and (b) AR and realized gain with different dimensions of the inner square patches, G2.

|S11

| (dB

)

–30

–20

–10

0

1.4 1.6 1.8 2.0 2.2 2.41.2Frequency (GHz)

G3 = 18mm, d1 = 4.5mmG3 = 19mm, d1 = 4.5mmG3 = 20mm, d1 = 4.5mmG3 = 19mm, d1 = 3.5mmG3 = 19mm, d1 = 5.5mm

(a)

0

3

6

9

12

15

AR

(dB)

1.55 1.60 1.65 1.70 1.751.50Frequency (GHz)

G3 = 18mm, d1 = 4.5mmG3 = 19mm, d1 = 4.5mmG3 = 20mm, d1 = 4.5mmG3 = 19mm, d1 = 3.5mmG3 = 19mm, d1 = 5.5mm

(b)

Figure 8: Variations of (a) |S11| and (b) AR with different dimensions of the center ring of the reflector, G3 and d1.

International Journal of Antennas and Propagation 7

*e prototype antenna was measured with AgilentE5071Cvector network analyzer for |S11| and for radiationpattern and AR in our anechoic chamber. *e results areshown in Figure 11 It can be seen that the measured resultsagree reasonably well with the simulated ones.*emeasured|S11| frequency band of − 10 dB is 1530MHz to 2280MHz

which covers the full operating bandwidth of BD2 B1, GPSL1, and GLONASS L1.

*e simulated and measured AR and gain are shown inFigure 12(a). *e measured 3 dB AR frequency ranges from1558MHz to 1672MHz in RHCP. *e measured resultsagree reasonably well with the simulated results. *e

|S11

| (dB

)

1.4 1.6 1.8 2.0 2.2 2.41.2Frequency (GHz)

–40

–30

–20

–10

0

G1 = 60.5mm, G4 = 25.5mmG1 = 65.5mm, G4 = 25.5mmG1 = 70.5mm, G4 = 25.5mmG1 = 65.5mm, G4 = 24.5mmG1 = 65.5mm, G4 = 26.5mm

(a)

1.55 1.60 1.65 1.70 1.751.50Frequency (GHz)

0

3

6

9

12

15

AR

(dB)

G1 = 60.5mm, G4 = 25.5mmG1 = 65.5mm, G4 = 25.5mmG1 = 70.5mm, G4 = 25.5mmG1 = 65.5mm, G4 = 24.5mmG1 = 65.5mm, G4 = 26.5mm

(b)

Figure 9: Variations of (a) |S11| and (b) AR with different dimensions of the outer ring of the reflector, G1 and G4.

(a) (b)

(c)

Figure 10: *e fabricated prototype of the proposed antenna. (a) Top view, (b) bottom view, and (c) side view.

8 International Journal of Antennas and Propagation

measured gain varies with frequency and the gain is 5.26,5.78, and 5.12 dBi at the center frequency of BD2 B1(1561MHz), GPS L1 (1575MHz), and GLONASS L1(1602MHz), respectively. *e maximum measured gain is5.87 dBi in the whole operating frequency band. *e sim-ulated and measured radiation efficiencies are shown inFigure 12(b). As can be seen, the measured radiation effi-ciencies are around 80%, while the simulated ones arearound 90%. *e discrepancy between simulations andmeasurements are mainly due to the errors of the con-ductivity of conductors and dielectric loss angle of tangent ofthe antenna between the theoretical values and the truevalues.

*e normalized RHCP and LHCP radiation patterns ofthe proposed antenna at the frequency of 1.561, 1.575, and1.602GHz in the xz plane and yz plane are simulated andmeasured, respectively, and the results are shown in

Figure 13. In all cases, the measured and simulated resultshave good corroborations.

Table 2 shows the comparison of the antenna size andperformance between the proposed antenna and other re-cently published works. Here, we introduce the ratios ofantenna volume size to relative bandwidth of |S11| and AR,RVB1, and RVB2, respectively; they are to measure therelative sizes of the antennas. Such ratio definitions forcomparisons are justifiable and representative since theantenna size is proportional to the frequency it operates at.*e smaller the ratio is, the better performance the antennahas in terms of the size.

As can be seen from Table 2, the proposed antenna hasthe smallest height of 0.033λ0 for profile and transverse areaof 0.33× 0.33 λ02, with the smaller ratio of 0.83 for RVB1 and4.9 for RVB2. *erefore, it is the compact antenna withbetter performance of IBW and ARBW.

|S11

| (dB

)

1.4 1.6 1.8 2.0 2.2 2.41.2Frequency (GHz)

SimulatedMeasured

–40

–30

–20

–10

0

Figure 11: Simulated and measured |S11| of the proposed antenna.

0

3

6

9

15

12

AR

(dB)

Gai

n (d

Bi)

0

2

4

6

1.57

1.64

1.63

1.62

1.65

1.56

1.60

1.59

1.58

1.66

1.67

1.61

Frequency (GHz)SimulatedMeasured

(a)

20

40

60

80

100

Radi

atio

n ef

ficie

ncy

(%)

1.57

1.64

1.63

1.62

1.65

1.56

1.60

1.59

1.58

1.66

1.67

1.61

Frequency (GHz)SimulatedMeasured

(b)

Figure 12: Measured and simulated results of (a) gain and AR at the boresight and (b) radiation efficiency.

International Journal of Antennas and Propagation 9

5. Conclusions

*e CPW feed slot antenna is combined with the modifiedreflector to develop a new compact low-profile antenna withunidirectional radiation for GNSS application. *e modified

reflector contains an inner square patch with four slantly cutcorners, a center ring, and an outer ring with a notch and hasa small transverse area of 0.33× 0.33 λ02. *e proposeddesign can significantly reduce the separation gap betweenthe radiator and the reflector and then result in a smaller

030

60

90

120

150180

210

240

270

300

330

xz planef = 1.561GHz

0

–5

–10

–15

–20

–15

–10

–5

0

(a)

030

60

90

120

150180

210

240

270

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330

yz planef = 1.561GHz

0

–5

–10

–15

–20

–15

–10

–5

0

(b)

030

60

90

120

150180

210

240

270

300

330

xz planef = 1.575GHz

0

–5

–10

–15

–20

–15

–10

–5

0

(c)

030

60

90

120

150180

210

240

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300

330

yz planef = 1.575GHz

0

–5

–10

–15

–20

–15

–10

–5

0

(d)

030

60

90

120

150180

210

240

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300

330

xz planef = 1.602GHz

0

–5

–10

–15

–20

–15

–10

–5

0

(e)

030

60

90

120

150180

210

240

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330

yz planef = 1.602GHz

0

–5

–10

–15

–20

–15

–10

–5

0

(f )

Figure 13: Simulated andmeasured radiation patterns in the xz plane and the yz plane at (a) f� 1.561GHz, (b) f� 1.575GHz, and (c) f� 1.602GHz.

10 International Journal of Antennas and Propagation

antenna profile of about λ0/30. It has a wide IBW and ARBWof 41.8% and 7.1%, respectively, and meanwhile, the peakmeasured gain can reach 5.87 dBi in the whole operatingfrequency band. In addition, its structure is easily fabricatedsince it has a simple CPW feed and does not need additionalfeeding networks and shorting probes. It may also be usedconveniently as an antenna array element because of its side-fed structure, low profile, and small size.

Data Availability

*e data used to support the findings of this study are in-cluded within the article.

Conflicts of Interest

*e authors declare that they have no conflicts of interest.

Acknowledgments

*is work was supported by the Natural Science Foundationof Fujian Province of China under Grant no. 2019J01638 andthe Science and Technology Project Plan of Fuzhou of Chinaunder Grant no. 2018-G-89.

References

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Table 2: Comparison of the antenna size and performance between this work and other recently published works.

Ref. no Height (λ0) Area (λ02) IBW (%) RVB1 (×10− 2) ARBW (%) RVB2 (×10− 2)[4] 0.13 0.45× 0.45 43.8 6.01 42.6 6.18[5] 0.042 0.88× 0.88 8.52 38.17 7 46.4[6] 0.096 0.6× 0.6 40.0 8.64 34.0 10.15[7] 0.09 0.7× 0.8 97.8 5.15 83.8 6.02[15] 0.076 0.44× 0.44 33.5 4.39 27.2 5.41[16] 0.22 0.54× 0.54 52.6 12.2 34.4 18.6[17] 0.22 0.85× 0.85 109.6 14.6 60.9 26.3*is work 0.033 0.3× 0.3 41.8 0.83 7.1 4.9Height� total profile height; area� area of the reflector; IBW� − 10 dB |S11| relative BW; RVBR1� ratio of antenna volume size to relative bandwidth of the |S11|; ARBW� 3 dB AR relative BW; RVB2� ratio of antenna volume size to relative bandwidth of the AR.

International Journal of Antennas and Propagation 11

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[19] R. Xu, J.-Y. Li, K. Wei, and G.-W. Yang, “A broadband slotantenna with unidirectional circularly polarized radiationpatterns,” IEEE Antennas and Wireless Propagation Letters,vol. 16, pp. 317–320, 2017.

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